The integration degree of integrated circuits is more and more intensified and in the production of a semiconductor substrate of VLSI, an ultrafine pattern comprising lines having q width of quarter-micron or less must be processed. For achieving refinement of a pattern, means of using an exposure light source having a shorter wavelength in the formation of a resist pattern is known.
For example, in the production of a semiconductor device having an integration degree of up to 64 M bits, the i-line (365 nm) of a high-pressure mercury lamp has been heretofore used as the light source until today. For the positive resist respondent to this light source, a large number of compositions comprising a novolak resin and a naphthoquinone diazide compound as a photosensitive material have been developed and succeeded in giving a satisfactory result in the processing of lines having a width of about 0.3 μm or more. In the production of a semiconductor device having an integration degree of 256 M-bits or more, a KrF excimer laser ray (248 nm) is employed as the exposure light source in place of the i-line.
Recently, for producing a semiconductor having an integration degree of 1 G-bit or more, an ArF excimer laser ray (193 nm) which is a light source having a short wavelength is used. Furthermore, use of an F2 excimer laser ray (157 nm) is being studied for forming a pattern of 0.1 μm or less.
To cope with this tendency toward shorter wavelength of the light source, the resist material is greatly changed in its constituent components and chemical structure. More specifically, conventional resists comprising a novolak resin and a naphthoquinonediazide compound have large absorption in the far ultraviolet region at 248 nm and therefore, the ray may fail in reaching the resist bottom to a sufficient depth, as a result, only a tapered pattern and low sensitivity is obtained.
In order to solve this problem, a so-called chemical amplification-type resist, that is, a composition mainly comprising a resin having a basic skeleton of poly(hydroxy-styrene) which shows small absorption in the region of 248 nm and is protected with an acid-decomposable group, and using in combination a compound (photoacid generator) capable of generating an acid upon irradiation with a far ultraviolet ray has been developed. In the chemical amplification-type resist, the acid generated in the exposed area causes a catalytic decomposition reaction and thereby changes the solubility in a developer, so that a high-sensitivity and high-resolution pattern can be formed.
However, the compound having an aromatic group originally has large absorption in the region at a wavelength of 193 nm and therefore, when an ArF excimer laser ray (193 nm) is used, even the above-described chemical amplification-type resist cannot provide sufficiently high performance.
To solve this problem, the acid decomposable resin having a basic skeleton of poly(hydroxystyrene) is replaced by an acid decomposable resin having incorporated into the main or side chain of the polymer an alicyclic structure having no absorption at 193 nm, with an attempt to improve the chemical amplification-type resist.
However, this alicyclic resin has large absorption in the region of 157 nm and therefore, with use of an F2 excimer laser ray (157 nm), is still deficient in obtaining an objective pattern of 0.1 μm or less. On the other hand, Proc. SPIE., Vol. 3678, page 13 (1999) has reported that a resin having incorporated thereinto a fluorine atom (perfluoro-structure) has sufficiently high transparency to light at 157 nm, and effective fluorine resin structures have been reported in Proc. SPIE., Vol. 3999, page 330 (2000), ibidem., page 357 (2000), ibidem., page 365 (2000) and WO-00/17712.
The resists comprising such a fluorine resin are, however, not always satisfied with respect to the dry etching resistance and since these resins show peculiar water repellency or oil repellency attributable to the perfluoro-structure, improvement of the coatability (uniformity of the coated surface) and prevention of development defects are being demanded.